(1) Field of Invention
The present document relates to a multi-level output comparator. In particular, the present document relates to a method and system for determining the voltage level of an input signal compared to a reference voltage.
(2) Description of the Prior Art
Comparators are electronic devices which compare an input voltage with a reference voltage (or an input current with a reference current), and provide at their output an indication which of the two voltages (or currents) is greater. Comparators may be designed based on operational amplifiers with a particularly high gain. Such comparators suffer, however, from lengthy recovery times from saturation of the operational amplifiers, thereby limiting the frequency at which comparisons may be performed. Furthermore, such comparators only provide a single output, i.e. a single comparison, with no indication on how much the input voltage deviates from the reference voltage.
Flash analogue-to-digital converters (ADCs) make use of a plurality of comparators, in order to provide a more detailed analysis on how much the input voltage deviates from the reference voltage. Typically, a flash ADC makes use of a linear voltage ladder (i.e. a voltage divider) which divides the reference voltage Vref into a sequence of sub-voltage values (e.g. Vref/2, Vref/4, Vref/8, etc.). Furthermore, the flash ADC comprises a plurality of comparators (e.g. comparators based on operational amplifiers) which compares the input voltage with each of the sequence of sub-voltage values, respectively. As a result, an indication is provided on how much the input voltage Vin deviates from the reference voltage. Flash ADCs are disadvantageous in that they require a large number of dedicated comparators. Furthermore, flash ADCs may have limited speed (as a result of the limited speed of the plurality of comparators).
The present document addresses the shortcomings of the above mentioned comparators and flash ADCs. In particular, the present document describes a comparator which can operate at high frequencies and which provides a plurality of outputs for a single input (i.e. which provides a direct information on how far the input voltage Vin deviates from the reference voltage Vref, without the need of a plurality of distinct comparator circuits). The plurality of outputs of the described comparator may be used to implement a window comparator, thereby providing an indication of the range voltage of the input voltage Vin.